Growth of high-quality spinel-structured metal oxide films on substrates is important in a variety of chemical, electronic, and magnetic applications. Many of the technological advances in this field have been in the techniques to grow high quality Fe3O4 (magnetite) thin films utilizing physical vapor deposition techniques such as plasma laser deposition (PLD) and molecular beam epitaxy (MBE), for example as disclosed in Lind et al. Phys. Rev. B 45 (4) 1838, 15 Jan. 1992 and Chambers, S.A. Surf. Sci. Rep. 39 (2000) 105. Less progress has been achieved, however, in producing high-quality spinel-structured metal oxide films having more than one metal constituent, such as the binary oxides of CoFe2O4 (Co ferrite), NiFe2O4 (Ni ferrite), and CoCr2O4 (Co chromite), and the ternary oxide of (Mn,Zn)Fe2O4. Co ferrite is of particular interest for a variety of next-generation magnetic read/write technologies because it exhibits magnetic properties that are significantly enhanced compared to those of other magnetic oxides.
Although the bulk properties of Co ferrite have been known for decades, thin film synthesis and characterization efforts have been limited. Suzuki et al. (1) (Appl. Phys. Lett. 68 (5) 714, 29 Jan. 1996), Suzuki et al. (2) (J. of Magnetism and Magnetic Materials 191 (1999) 1), and Hu et al. (Phys. Rev. B 62 (2) R779, 1 Jul. 2000) disclose PLD techniques to grow Co ferrite on a variety of substrates, including MgO, SrTiO3 and MgAl2O4. Hu et al. asserts that epitaxial Co ferrite of high magnetic and structural quality cannot be grown without the use of a complex crystal symmetry and lattice parameter matching scheme involving the use of buffer layer, such as CoCr2O4, on substrates such as MgAl2O4. Substrates of different symmetry, such as MgO, are thought to result in the nucleation and growth of Co ferrite that has high concentrations of a particular structural defect called an antiphase boundary, and that the presence of these defects compromises the magnetic properties. Even with these more complex substrate/buffer layer combinations, a post-growth anneal is required to obtain the desired structural and magnetic properties when PLD is used as the growth method. Furthermore, PLD-grown film surfaces show considerable roughness (see FIG. 1 of Suzuki et al. (2)) which precludes the formation of laminar film structures and superlattices.
Further improvement in current methods, however, is necessary if magnetic spinels are to be broadly useful in magnetic media applications. Desirable properties include hysteretic magnetization loops and atomically flat films grown on simple substrates, such as MgO. PLD has not produced Co ferrite with these desirable properties. Accordingly, there is a need for an improved process for epitaxially growing a spinel-structured metal oxide on a substrate.